1. Technical Field of the Invention
The present invention relates to a polishing pad conditioner that conditions a polishing pad.
2. Prior Art
FIG. 1 is a schematic view showing a CMP apparatus (Chemical Mechanical Polishing Apparatus) used in a final process for producing deviced/bare silicon wafers. The CMP apparatus is composed of a rotating base plate 3 with a polishing pad 2 mounted thereon, and a rotating plate 4 on the lower surface of which a silicon wafer 1 is fixed; while the rotating base plate 3 and the rotating spindle 4 are rotated around their respective axes, a slurry 5 containing colloidal silica is fed between the plate 3 and spindle 4, and super-fine particles of SiO2 (with grain diameters of several nanometers to several tens of nanometers) in the colloidal silica react with the silicon wafer (Si) and this softens the particles, and at the same time, the lower surface of the silicon wafer 1 is polished by the SiO2 in the colloidal silica retained on the polishing pad.
The upper surface of the polishing pad 2 used in the CMP apparatus should have an appropriate roughness so that a preferred amount of slurry 5 is held in the space between the pad and the silicon wafer 1 and a suitable amount of friction is produced between the pad and the silicon wafer 1. However, when the CMP apparatus is used continuously, the roughness of the upper surface of the polishing pad is gradually lost, and the surface becomes slippery like a mirror, and eventually the polishing rate is greatly reduced and efficient polishing can no longer be performed.
Therefore, the surface of the polishing pad must be reprocessed (in a process called conditioning) to restore the appropriate roughness, and a polishing pad conditioner, an example of which is shown in FIGS. 2A and 2B, has conventionally been used.
FIG. 2A shows an electrodeposition grindstone in which the abrasive grains 8 (for instance, diamond abrasive grains with a grain diameter of several tens of microns) are fixed to the lower surface of a base metal 6 by a plated layer 7 of Ni etc. However, this polishing pad conditioner used to suffer from the fact that the abrasive grains 8 could be attached by only one layer of plating and the strength with which they were held by the metal plating was low. Consequently, because some of the abrasive grains 8 come off, the life is short and the operation can only be repeated a few times. And moreover, the detached abrasive grains are left on and become embedded in the polishing pad (which is for instance, made of a plastic material), with the problem that the silicon wafer 1 is damaged. Another problem was that due to the residue of heavy metal remaining after the plating process, the high-purity silicon wafer 1 was contaminated.
FIG. 2B shows another polishing pad conditioner in which the lower surface of the base metal 6 is formed with an appropriate roughness in advance, and then its surface is coated with a thin diamond film 9 by CVD (Chemical Vapor Deposition). Although the thin film 9 of this polishing pad conditioner provides a high adhesive force, the time taken to grow the film is so long that the manufacturing cost is extremely high and this is a practical problem. In addition, there are other problems with this conditioner including the difficulty in obtaining a uniform film thickness and the short life due to the extremely thin film (several tens of microns).
The present invention aims at solving the various problems described above. More explicitly, the objects of the present invention are to provide a polishing pad conditioner that can reprocess (condition) the surface of a polishing pad so as to give it an extremely long life, that is capable of maintaining an even conditioning power, with a rather low manufacturing cost, and without the risk of contaminating the silicon wafer.
As modern science and technology have made great advances, the requirements for ultra-high-precision processing have rapidly become more and more rigorous, and for example, the Electrolytic In-process Dressing (ELID) process was developed by the applicants of the present invention and has been disclosed (Institute of Physical and Chemical Research, Symposium xe2x80x9cTrends in Advanced Technologies for Mirror Surface Polishing,xe2x80x9d held Mar. 5, 1991).
According to this ELID method, a conducting grindstone is used in place of the electrode used in conventional electrolytic grinding, and an electrode is provided opposite the grindstone with a gap between them, and while a conducting liquid flows between the grindstone and the electrode, a voltage is applied between the grindstone and the electrode, and by dressing the grindstone with the electrolyte, the workpiece is ground by the grindstone. With this ELID grinding method, even if the abrasive grains are fine, loading of the grindstone is prevented due to the electrolytic dressing, therefore by using the abrasive grains finer, a very excellent processed surface such as a mirror surface can be produced by the ELID grinding process. Consequently, it is expected that the ELID method will be applied to various grinding processes, because with this method, the sharpness of the grindstone can be maintained from high-efficiency grinding to mirror-surface grinding, and a highly accurate surface that could not be produced by conventional technologies can be created in a short time.
The present invention is aimed at greatly improving the performance of a polishing pad conditioner using the principles of this ELID method. In detail, in the present invention, a plurality of diamond prisms (12) are arranged so as to project towards a surface to be processed, and a conducting bonding material (14) fixes the aforementioned diamond prisms into a single body; the above-mentioned conducting bonding material can be dressed electrolytically by making a conducting liquid (24) flow in the gap between the bonding material and an electrode (22) opposite the bonding material.
According to the aforementioned configuration of the present invention, because the conducting bonding material (14) that fixes the diamond prisms into a single body can be dressed electrolytically with the flow of conducting liquid (24) to the electrode (22) placed opposite the body, when the tips of the diamond prisms (12) wear resulting in a reduced protrusion thereof from the conducting bonding material and a deterioration in the conditioning capability, an amount of the material is removed from the surface thereof by electrolytic dressing, thereby increasing the amount by which the diamond prisms protrude from the surface. Accordingly, the amount of protrusion can be optimized at all times, so the tips of the diamond prisms can always function as cutting edges, therefore a polishing pad (made of a plastic material, for instance) can be reconditioned to an appropriate roughness, hence the conditioning performance can be maintained at a stable, uniform level. In addition, since artificial prismatic diamonds with a length of about 2 mm can be used as the diamond prisms, the life is several tens of times as long as those of conventional abrasive grains or thin-film conditioners.
According to a preferred embodiment of the present invention, the above-mentioned conducting bonding material (14) is composed of a conducting metal sheet (15) with a plurality of holes (15a) in which the diamond prisms (12) are embedded, and a conducting sintered metal (16) is filled into the gap between the aforementioned holes and the diamond prisms and sintered.
According to this configuration, the diamond prisms (12) are inserted into the holes (15a), and a conducting metal powder is placed in the gaps and sintered, thus a conducting sintered metal (16) that firmly holds the diamond prisms (12) can be formed, so compared to the slow-growing, expensive CVD method, the manufacturing cost can drastically be reduced. In addition, because the metal powder can be sintered while being maintained at a high temperature in an inert gas environment, there is no risk of impurities getting mixed in, therefore the silicon wafer can be protected from contamination.
The above-mentioned conducting bonding material (14) is shaped as a circular disk, and tips of the aforementioned plurality of diamond prisms are located on the bottom surface of the disk. The material in this configuration can be used as a circular-disk-type polishing pad conditioner.
Other objects and advantages of the present invention are revealed in the following description referring to the attached drawings.